1. Field of the Invention
The present invention relates to a method of manufacturing a hydrogen transport membrane and the article itself. More specifically, the invention relates to producing a membrane substrate, where the ceramic substrate is coated with a metal oxide slurry, thereby eliminating the need for an activation step prior to coating the ceramic substrate through an electroless plating process. The metal oxide slurry also allows the pore size and porosity of the membrane substrate to be modified by controlling the extent of oxidation or reduction of the metal oxide deposited by the slurry.
2. Description of Related Art
Composite hydrogen transport membranes are used to separate hydrogen from a hydrogen containing feed for a variety of industrial processes. Such composite membranes can consist of a hydrogen transport material or membrane supported by a porous support such as a ceramic. Conventional processing and manufacturing techniques for hydrogen transport membranes require an activation step to provide active sites on the porous substrate prior to the application of a membrane onto the substrate in order for the membrane (or thin layer) to separate the hydrogen containing feed gas for a variety of industrial applications. Typically, this activation step requires the use of hazardous chemicals, additional processing steps, and prolongation of the fabrication time prior to the application of the membrane, which is typically applied through an electroless plating process.
In the related art, the substrate of the hydrogen transport membrane is prepared by sensitizing and activating it prior to the electroless plating. For example, U.S. Pat. No. 7,175,694 B2 to Ma et al. discloses the surface of a substrate should be sensitized and activated by aqueous tin chloride (SnCl2) and palladium chloride (PdCl2) solutions to seed Pd nuclei on the substrate before plating and this process should be repeated between two and ten times. It further discloses that a substrate could be plated without an activation step, but it resulted in a slow process extending time for plating.
In U.S. Pat. No. 6,761,929 B2 to Damle, the surface plated was sensitized with a sensitizing solution (tin chloride in hydrochloric acid) and activated with an activating solution (palladium chloride in hydrochloric acid) before plating.
Ind. Eng. Chem. Res. (38) 1925-1936, 1990 “A New Preparation Technique for Pd/Alumina Membranes with Enhanced High-Temperature Stability” by Paglieri et al discloses conventional and new methods for surface activation before plating. The conventional one used SnCl2 and PdCl2, while the new one used a palladium acetate solution followed by a heat treatment under H2 environment. However, both methods still needed an activation step before plating.
U.S. Pat. No. 8,101,243 B2 to Way et al. describes making palladium-gold alloy membranes on porous supports. The electroless plating method used for depositing the alloy requires an activation step to seed the substrate with palladium crystals by any of a variety of methods, including impregnating with a solution of palladium acetate or another salt. Substrates manufactured with metallic crystals embedded in them or using metals other than palladium to seed plating are not considered.
U.S. Pat. Nos. 7,604,771 and 7,959,716 to Song et al. describe an increase in hydrogen flux with reduction of metal oxides used in membrane substrates. These oxides can be either mixed oxides, such as Sr—Fe—Co—O or NiO. These metal oxides were part of the substrate, not used as a surface coating. U.S. Patent Application Publication No. 2007/0044663 to Song et al. describes a substrate made from NiO/TZ-3Y, where TZ-3Y is partially stabilized zirconia. The nickel content in the substrate was about 50%. They showed that reducing the substrate caused pore size and hydrogen flux to increase.
Others have seen an effect of nickel oxide particles on pore size and porosity in solid oxide fuel cells (SOFC), but not with respect to using nickel oxide to produce hydrogen transport membranes. For example, Minerals Engineering (21) 157-166, 2008, “The characterization of nickel metal pore structures and the measurement of intrinsic reaction rate during the reduction of nickel oxide in H2—N2 and H2—H2O atmospheres” by Hidayat et al. investigated the reduction of NiO in hydrogen mixtures at high temperature using scanning electron microscopes and observed a high volume fraction of micro-sized pores with nickel metal after reducing a NiO sheet in a stream of pure H2 and mixtures of H2—N2 and H2—H2O.
ECS Transactions (25) 1985-1992, 2009 “In situ Reduction and Oxidation of Nickel from Solid Oxide Fuel Cells in a Transmission Electron Microscope” by Faes et al. discloses the basic idea concerning the effect of in situ reduction on NiO that is used as an electrolyte-supporting anode in SOFC. The reduction results in an increase in the anode porosity because of volume contraction between NiO and metallic Ni.
To overcome the disadvantages of the related art, it is an object of the present invention to eliminate the activation step required in electroless plating and significantly reduce processing time and costs. The present invention produces essentially same quality membranes and eliminates the activation step typically required before electroless plating.
It is also an object of the invention to produce a substrate where the pore size and porosity can be modified by oxidation and/or reduction of the surface so that the pore size and porosity are suitable for electroless plating, increasing membrane yield by enabling some substrates with pore sizes that are outside the acceptable range to be modified so that the pore sizes are appropriate and allowing minor modification of acceptable substrates to optimize membrane performance. It is a further object of the invention to provide a slurry employed in the treatment of the substrate to enable pore size modification while also eliminating the use of hazardous chemicals used for activation and eliminating processing steps in membrane production. It is yet another object of the invention to provide a composite membrane manufactured using the inventive process where the membrane is employed to separate a desired permeate, such as hydrogen, from a stream comprising the desired permeate and other materials. Further, it is an object of the invention to provide a membrane article to perform the desired separation.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art upon review of the specification, drawings and claims appended hereto.